The present invention relates to an improved perlite-based insulation board especially designed for use in roof insulation systems, such as, but not limited to, built-up, modified bitumen and single ply roofing systems. Perlite-based insulation board has certain advantages over other types of insulation board used in roof insulation systems, such as wood-fiber, glass fiber and polymer foam insulation board. For example, perlite-based insulation board typically is lower in density and absorbs less water than either wood-fiber or glass fiber insulation board and the high inorganic content of the perlite-based insulation board renders it less flammable than either wood-fiber or polymer foam insulation board.
Perlite-based insulation boards, such as the perlite-based insulation boards marketed by Johns Manville International, Inc. under the trademark "FESCO", and retro-fit perlite based insulation boards have been commercially available for decades. These perlite-based insulation boards are highly satisfactory insulating products that are well adapted for use as insulation boards in built-up, modified bitumen and single ply roofing systems. These perlite-based insulation boards provide good thermal performance; are relatively low in density (generally ranging from about 8 to about 15 pounds per cubic foot); and exhibit good break load and flexural strength as well as good compressive resistance. These perlite-based insulation boards are also resistant to fire and water absorption and possess other desirable physical properties. The insulation board for roofing systems disclosed in U.S. Pat. No. 4,126,512, issued on Nov. 21, 1978, and entitled Perlitic Insulating Board, is representative of these types of perlite-based insulation boards and the disclosure of this patent is hereby incorporated by reference.
Other than expanded perlite, which constitutes between about 50% and about 76% by dry weight of these insulation boards, these perlite-based insulation boards comprise in the finished product between about 15% and about 45% by dry weight cellulosic fiber; between about 1% and about 5% by dry weight starch binder; between about 2% and about 9% by dry weight bituminous material to increase the insulation board's resistance to water absorption and about 0% to about 3% by dry weight alum.
While the above discussed perlite-based insulation boards perform very well, there has remained a need to improve the strength of such insulation boards and, preferably, without increasing or significantly increasing the water absorptivity of the insulation boards. Furthermore, since the perlite-based insulation boards are formed from an aqueous slurry containing the board ingredients in a continuous wet-laid process on free-draining equipment, such as a Fourdrinier machine, and subsequently, dried in an oven, any increase in the water retention of the boards delivered to the oven for drying can increase the manufacturing costs of the perlite-based insulation boards due to an increase in gas consumption in the drying process. Thus, it would be desirable to increase the strength of the perlite-based insulation boards with little or no increase in either the water absorptivity of the finished product or the water retention of the boards delivered to the oven for drying.